1. Field of the Invention
The present invention is in the field of drafting templates and guides. More particularly, this invention presents means to enable a draftsman to draw a series of related ellipses with high precision and without damage to the drafting medium.
2. Description of the Prior Art
Generally speaking, anyone can generate an ellipse by placing pins in a drafting medium at the foci of the ellipse, and, using a pencil, draw any number of ellipses by maintaining the pencil within a taut loop of string passing around the pins. More reasonably, however, a template is used, both for ease and to avoid damage to the drafting medium, as well as to facilitate the productivity of the draftsman. At the same time, professional drawing-board experience is essential in using a guide for drawing related ellipses of increasing or decreasing size and varying eccentricity for inking in drawings. In drawing such families of ellipses, it is difficult even for the experienced professional draftsman to obtain, e.g., 0.8-millimeter (mm) accuracy in spacing between circles, especially when inking-in is required.
Currently, when a professional draftsman is confronted with the problem of drawing a series of related ellipses, he has his choice of using various templates of the existing art, all of which have drawbacks.
In using a template, each succeeding figure must be located appropriately by means of coordinating lines adjacent the hole in the template chosen for use; however, no matter how careful the draftsman is, he is never completely sure that each succeeding figure is precisely aligned. Further, the range of sizes available with current templates is somewhat restricted. In some cases, the lack of precision drawings can be critical, especially, as noted, where those drawings are used for shop and field work or in the presentation of patent illustrations. When the distance between adjacent figures approaches the thickness of the inked line, maintaining proper relationship with existing templates also becomes marginal.
Another problem encountered with the apparatus and methods of the prior art is that a required series of ellipses to be drawn must be carefully planned. Generally, the smallest ellipse is drawn first, followed by those of increasing size. An attempt to proceed in the opposite fashion is difficult because the template, even though substantially transparent, often at least partly obscures the larger ellipse in the attempt to align the smaller. In the event that the draftsman discovers that he has to draw a series of ellipses congruent with one already drawn because of a change in specifications or for other reasons, it is not uncommon to have to remove the earlier-drawn figures and begin over. In the case where the ellipse has already been inked, the job becomes very difficult, and potentially damaging to the drafting medium.
Irrespective of the planning required in drawing ellipses with existing templates, a further problem arises where the range of the sizes of ellipses to be drawn is fairly great. Current practice requires the use of several templates, with the problems of careful alignment as already noted; further to that, however, is the circumstance that different templates may have different kinds of reference marks, which then requires that the draftsman pay particular attention to how he is aligning the template in order to avoid imprecision in the drawing.
While none of the problems discussed here are insurmountable, they are time-consuming, and detract from the productivity of the draftsman.
Even if the foregoing problems can be avoided, the draftsman now faces the problem of inking the pencil drawing without smearing the lines. Using templates of the prior art, the draftsman has to be careful not to permit the pen to contact the line where the template rests on the paper, or the ink will spread into that line by capillary action, causing his line to be thicker than he wants, even assuming that he is able to control its actual placement with the necessary precision in the first place.
In present practice, when a draftsman makes an inked ellipse with a template, he places some kind of shim under the template to prevent its direct contact with the drawing medium to avoid capillarity. The use of the shim, however, invites both inaccuracy in the dimension of the ellipse and slippage of the template on the shim. To avoid the latter problem, the draftsman can tape the two together, but then tends to lose whatever time advantage he has gained by the use of the template.
Furuoka, in U.S. Pat. No. 3,568,327, shows what is essentially an amusement device for the production of epicyclic, hypocyclic and similar figures generated by the interrelation of a fixed reference point with another, moving point. By its very nature, the Furuoka device is incapable of producing related ellipses except by moving the template, a problem discussed hereinabove. The Furuoka apparatus further has means whereby the position of the template is fixed at specified angular intervals.
A device similar to that of Furuoka is described by Siegel in U.S. Pat. No. 3,699,660, differing from Furuoka in that it is adjustable to permit infinite variation among the designs generated. The Siegel device, however, is also limited in that it requires movement of the entire device to permit drawing of curvilinear figures related in size, but with a commonality of center or focus, thereby leading to the imprecision described hereinabove.
Jordan, in U.S. Pat. No. Des. 165,849, shows a drafting template whereby lines can be drawn at variable angles to an initial reference point or line. Use of the Jordan template requires the removal and replacement of screws to permit the template to be changed or the angle of a particular line altered.
None of the references discussed herein makes any provision for inking of a precision drawing, nor do they provide for the construction of a plurality of elliptical figures without regard to the order in which the figures are drawn.